Yarn process



Patented July 29, 1952 YARN PROCESS Harold Henry Hebeler, Eggertsville, N. Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del.

No Drawing. Application August 23, 1950, Serial No. 181,092

3 Claims. 1

This invention relates to a process for spinning synthetic linear polyesters and is more particularly concerned with a high-speed process for melt-spinning polyethylene terephthalate material to produce useful as-spun fibers and yarns.

The preparation of useful synthetic linear textile fibers by previous melt-spinning processes has required the two separate operations of spinning and then drawing. Melt-spun fibers of synthetic linear polyesters and polyamides in the as-spun state havepreviously been very weak and not suitable for textile uses, except in very special applications, until drawn. The as-spun tenacities have been in the range of 0.2 to 0.8 grams per denier, at elongations of several hundred per cent. By a subsequent drawing operation, in which both orientation and crystallization occur, useful fibers are obtained having tenacities in the range of 4 to 10 grams per denier at elongations of 5 to This is generally true for synthetic yarns made from condensation or addition polymers.

It is apparent that considerable economic advantage would be achieved by providing a process which produces useful as-spun fibers. Elimination of the drawing operation subsequent to the normal spinning process would result in a considerable saving in both manpower and equipment and would speed up production considerably. Furthermore, for a given production capacity less space would be necessary, since the area currently needed for drawing yarn would be eliminated.

It is an object of the present invention to provide a process for. melt-spinning polyethylene terephthalate material at high speeds to produce useful as-spun high tenacity fibers and yarns having low shrinkage without the necessity of a,

subsequent drawing operation. Other objects of the invention will become apparent from the following description and claims.

The objects of this invention are accomplished by a process which comprises extruding a molten fiber-forming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret and pulling the extruded fibers away from the spinneret by winding up or forwarding the fibers to the next operation at a spinning speed, measured after the fibers have completely solidified, in excess of 5200 yards per minute. By means of this process, yarns are prepared having tenacities of at least 3 grams per denier and shrinkages of about 4% or less in the as-spun state.

,By "fiber-forming material is meant an ethylene terephthalate polymer which preferably has an intrinsic viscosity of at least 0.3, since polymers having lower intrinsic viscosities are essentially non-fiber forming. The expression intrinsic viscosity is used herein as a measure of the degree of polymerization of the polyester and may be defined as wherein r is the viscosity of a dilute solution of the polyester in a mixture of 60 parts phenol and 40 parts tetrachloroethane, divided by the viscosity of the phenol-tetrachloroethane mixture per se, measured in the same units at the same temperature, and C is the concentration in grams of polyester per cc. of solution.

The fiber-forming material is principally polyethylene terephthalate, but the inclusion therein of up to 10 mol percent of modifying materials is intended whenever the expression polyethylene terephthalate material is used. Polyethylene terephthalate itself is a polycondensation product of ethylene glycol and terephthalic acid or an ester forming derivative thereof. During the preparation of this polyester, minor amounts of a modifying material may be added, e. g., another glycol and/or another dicarboxylic acid. Thus. a suitable funicular structure comprised essentially of polyethylene terephthalate may have included in the polymer molecule up to 10 mol percent of another glycol, such as diethylene glycol, tetramethylene glycol, or hexamethylene glycol. Or again, the molecule may contain up to 10 mol percent of another acid. As suitable examples of Limit modifying acids, there may be mentioned hexahydroterephthalic acid, bibenzoic acid, adipic acid, sebacic acid, azelaic acid, the naphthalic acids, 2,5-dimethyl terephthallc acid and bis-p-carboxy phenoxy-ethane.

These modifiers may be added as one of the initial reactants during the polymerization process, but the modifying materials may also be polymerized separately and then melt-blended with the polyethylene terephthalate. In either case the total amount of modifier in the final polymeric material should not exceed 10 mol percent. While the polymerization process is preferably carried out in the melt, it may also be performed in the solid phase, or in solution or emulsion by conventional procedures. An explanation of suitable polymerization processes for the type of polyesters comprehended herein is contained in United States Patent No. 2,465,319 to Whinfield and Dickson.

By spinning speed is meant the speed of the yarn at a point after complete solidification has occurred when no more reduction in denier is being observed. A convenient point for determining this speed is at the wind-up or forwarding regions. It will be obvious that the speed of an extruded polymer stream will not be the same while in the fluid or semi-fluid state as it is at the wind-up or forwarding place.

In preparing the useful high tenacity, low .shrinkage yarns by this invention, the following general procedure is used. The polymer, prepared by a conventional polymerization process, is cooled, broken into chips and dried. The chips are then melted on a heated grid and pumped by means of a metering pump of the type commonly :used in the synthetic textile industry through a filter pack and spinneret orifices into room temperature air. The extruded filaments cool and solidify by passage through the air and are subjected after solidification to a means for forwarding them at speeds in excess of 5200 yards per minute. The forwarding means may comprise a high speed wheel, roll or pinch rolls, an air jet or other suitable means. Under the impetus imposed by the forwarding means, the filaments elongate in the distance between the spinneret face and the point of complete solidification. The inertia of the material and the drag of the surrounding air apparently supplies sufficient tension in the form of drag on the filaments to induce orientation of the polymer molecules in the solidification range. Actually, no useful orientation takes place until the filamentary streams begin to solidify. The filaments for several inches from the spinneret appear to be just dangling from the spinneret. In the solidification range, the filaments can be seen to accelerate and become taut fibers, moving along their length at high speeds. The phenomenon can further be detected byfeeling the air dragged along with the filaments beginning at the solidification range. It is the orientation that takes place at this point which accounts for the useful properties of the yarn spun by the process of this invention.

' The properties of polyethylene terephthalate yarns spun under various conditions in accordance with the present invention are given in the table. The general procedure described was followed, with specific conditions as shown in the table. Spinning speed is given in yards per minute, tenacity is in grams per denier, and intrinsic viscosity is as defined previously. The percent shrinkage was calculated from the difference in length between fibers as-spun and boiled 4 August 23, 1950. Still lower spinning speeds produce low tenacity yarns having very high shrinkages, which approach the properties of conventional unoriented, as-spun polyesters or polyamides when the speed is reduced below 1500 yards per minute.

Above 5200 yards per minute the spinning speed can be increased up to speeds where excessive filament breakage occurs. For example, at extrusion rates of 15,000 denyards (denier times yards per minute), the upper limit is about 6500 yards per minute. At higher extrusion rates, the spinning speed can also be higher without excessive filament breaking at the spinneret. The upper practical limit for extrusion rate is about 41,000 denyards per spinneret hole.

The spinning speeds essential in the process of this invention may be obtained by several methods. There may be used a driven bobbin, a high s eed pirn take-up, or an air jet may be used as a tensiom'ng and forwarding device so that the yarn can be forwarded directly to a staple cutter without an intermediate wind-up.

The molten polymer may be extruded through a spinneret at temperatures within the range of 260 to 310 C. For optimum results this extrusion temperature should be between 280 to 295 C., although properties of the final yarn vary but little over the entire range. The preferred temperature range is from 10 to 20 C. lower than copolymers of ethylene terephthalate are used, depending on the copolymer, and typically in the range of'from 270 to 285 C.

When the molten polymer is extruded into room temperature air, the resulting filaments should be allowed to travel at least 45-50 inches before they reach the forwarding means. This distance is required for complete solidification. When the distance is in the range of 30-40 inches, fused filaments often result with an otherwise standard spinning procedure because of inadequate quenching time.

The outstanding advantage of the present invention is that valuable polyethylene terephthalate fibers and yarns having high tenacity and low shrinkage, are produced directly in the asspun condition without the necessity of an afterdrawing operation. The spinning process also operates at exceptionally high speeds. Both of these advantage contribute to increased production and a considerable saving in manpower and equipment.

The high tenacity, low shrinkage yarns produced by the process of this invention have great z utility in the apparel, industrial, and other fields. in water for five minutes. For example, in the apparel field, they may be Intrinsic Extrusion Denier Percent Percent Example Viscos- Temp. 5 2 5? per flla- 3 Elon- Shrinkity (O.) ment y gation age The spinning speed can be varied over a wide range above 5200 yards per minute. Lower spinning speeds in the range of from 3000 to 5200 1 yards per minute result in high shrinkage yarns of quite different properties, which spontaneously crimp to a wool-like resiliency upon heating in a relaxed condition, as disclosed in'detail in'my ..copending application, Serial No. 181,091, filed steam, compressed air and the like. Polyethylene terephthalate yarns also find use in blanket bindings, table cloths, Slip covers, theatre curtains, sails, lace, fishing lines, chair seats, lamp shades, deck chair fabrics, shoe fabrics, upholstery both flat and plush, veilings, and velvets.

As different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific processes disclosed except as defined in the appended claims.

What is claimed is:

1. A process for producing tenacious as-spun fibers which comprises extruding a molten fiberforming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and pulling the extruded material away from the spinneret at a spinning speed, measured afterthe material has com pletely solidified to a fiber, in excess of 5200 yards per minute and below speeds where excessive filament breakage occurs, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired;

2. A process for producing tenacious, as-spun fibers which comprises extruding, at a temperature within the range of from 260' to 310 C., a

molten fiber-forming material containing at least 90 mol percent of polyethylene terephthalate through a. spinneret, cooling the extruded material until solidified to a fiber, and pulling the extruded material away from the spinneret at a spinning speed, measured after the material has completely solidified to a fiber, in excess of 5200 yards per minute and below speeds where excessive filament breakage occurs, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

3. A process for producing tenacious, as-spun fibers which comprises extruding, at a temperature within the range of from 270 to 295 C., a molten fiber-forming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and pulling the extruded material away from the spinneret at a spinning speed, measured after the material has completely solidified to a fiber, in excess of 5200 yards per minute andbelow speeds where excessive filament breakage occurs, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

HAROLD HENRY HEBELER.

, file of this patent:

UNITED STATES PATENTS Number Name Date Whinfield et al Mar. 22, 1949 

1. A PRCOESS FOR PRODUCING TENACIOUS AS-SPUN FIBERS WHICH COMPRISES EXTRUDING A MOLTEN FIBERFORMING MATERIAL CONTAINING AT LEAST 90 MOL PERCENT OF POLYETHYLENE TEREPHTHALATE THROUGH A SPINNERET, COOLING THE EXTRUDED MATERIAL UNTIL SOLIDIFIED TO A FIBER, AND PULLING THE EXTRUDED MATERIAL AWAY FROM THE SPINNERET AT A SPINNING SPEED, MEASURED AFTER THE MATERIAL HAS COMPLETELY SOLIDIFIED TO A FIBER IN EXCESS OF 5200 YARDS PER MINUTE AND BELOW SPEEDS WHERE EXCESSIVE FILAMENT BREAKAGE OCCURS, SAID EXTRUDING BEING AT A RATE IN DENYARDS EQUAL TO THE PRODUCT OF SAID SPINNING SPEED AND THE SPUN DENIER DESIRED. 